1. Field of the Invention
The present invention relates generally to a method for regulating the flow of coolant to a heat exchanger in an automotive vehicle. More particularly, the present invention relates to a method wherein a reversible-flow pump is used in conjunction with a main fluid pump to regulate the coolant flow.
2. Disclosure Information
As automotive engines become increasingly more efficient, the amount of waste heat produced is being minimized. One result of this efficiency is that it is becoming more difficult to heat the passenger compartment of the vehicle. Auxiliary heaters, such as fuel fired heaters, and systems such as exhaust heat recovery systems which use heat recovered from the exhaust system of the vehicle are being used to warm the vehicle passenger cabin. However, these solutions tend to be expensive.
Another solution to the problem of providing more heat to a vehicle passenger compartment is to increase the amount of heated water sent to a heat exchanger, typically a heater core, over which ambient or recirculated air is passed prior to entering the cabin. In a typical heating system, a "water pump" circulates coolant through the vehicle engine to cool the engine. The coolant becomes hot and is directed to the heater core. A valve may regulate the amount of coolant entering the core. Air is passed over the core and becomes warm. The speed of the pump is controlled by the speed of the engine. As the engine speed increases, the amount of fluid delivered by the pump increases. This increase in fluid delivered to the heater core can damage the core due to erosion from the high velocity of the flow.
Current automotive industry practice for controlling fluid flow to the heater core to minimize erosion is to insert a variable restriction device or a bypass valve to reduce coolant flow at high engine speed. FIG. 1 shows the general relationship between heater core output (in BTUs) and coolant flow rate (in gallons per minute). As shown in FIG. 1, for optimum heater performance, the coolant supply should be about four gallons per minute. A flow rate greater than four gallons per minute will have little or no performance benefit while flow rates above eight gallons per minute may cause erosion of the heater core. The heater core will function adequately at a flow rate of between 2-4 gallons per minute. At flow rates below two gallons per minute, the heating system will not provide enough heat to maintain cabin comfort under all conditions. This condition occurs when the engine speed drops below about 1000 rpm in vehicles with fluid flow restrictors because the restrictor impedes fluid flow at all times. Vehicle occupants will notice the interior temperature drop when idling at a stop light and defroster performance will be poor.
Therefore, there is a need for a method and system for regulating coolant flow to a heater core which will provide adequate flow rates for producing adequate heat without damaging the heater core. It is an object of the present invention to provide a system which eliminates mechanical restriction devices so that increased fluid flow is produced at low engine speeds but which prevents heater core erosion at high engine speeds.